小于1平滑 加入λ系数 T训练数据,V词表,w:词 预测p'(wh)=(c(h,w)+)(c(h)+V),<1 特别非条件分布时p(w)=(c(w)+)/(T+V 举例:T< s>What is it what is small!T8 V=what, is, it, small,, <s>, flying, birds, are, a, bird,,V=12 p(it)=0.125,p(wha)=0.25,p()=0,p( what is it?)=0.252*0.1252≈0.001 p( It is flying)=0.125*0.25*02=0 取λ=0.1 p(it)=0.12,p(what=0.23p()=0.01, p( what is it?)=0232*0.122≈0007 p( it is flying)=0.2*0.23*0.012≈000003小于1平滑 • 加入λ系数 -T:训练数据,V:词表,w: 词 预测 p’(w|h)=(c(h,w)+λ)/(c(h)+ λ |V|), λ<1 特别:非条件分布时p’(w)=(c(w)+ λ)/(|T|+ λ |V|) • 举例：T: <s>what is it what is small? |T|=8 – V={what,is,it,small,?,<s>,flying,birds,are,a,bird,.}, |V|=12 – p(it)=0.125, p(what)=0.25, p(.)=0, p(what is it?)=0.252 *0.1252≈ 0.001 p(it is flying.)=0.125*0.25*02=0 – 取 λ=0.1 – p’(it)=0.12, p’(what)=0.23,p’(.)=0.01, – p’(what is it?)=0.232*0.122 ≈0.0007 p’(it is flying.)=0.12*0.23*0.012 ≈0.000003